A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs). Enhancements to LTE systems are considered so that they can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard. Multiple access in the downlink is achieved by assigning different sub-bands (i.e., groups of subcarriers, denoted as resource blocks (RBs)) of the system bandwidth to individual users based on their existing channel condition. In LTE networks, Physical Downlink Control Channel (PDCCH) is used for dynamic downlink scheduling. Typically, PDCCH can be configured to occupy the first one, two, or three OFDM symbols in a subframe of each radio frame.
The signal bandwidth for next generation 5G new radio (NR) systems is estimated to increase to up to hundreds of MHz for below 6 GHz bands and even to values of GHz in case of millimeter wave bands. Furthermore, the NR peak rate requirement can be up to 20 Gbps, which is more than ten times of LTE. Three main applications in 5G NR system include enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communications (URLLC), and massive Machine-Type Communication (MTC) under milli-meter wave technology, small cell access, and unlicensed spectrum transmission. Multiplexing of eMBB & URLLC within a carrier is also supported.
A plurality of physical resource blocks (PRBs) is allocated for PDCCH transmission that carry downlink control information (DCI). PDCCH for next generation NR systems is referred to as NR-PDCCH. In order to decode NR-PDCCH targeted specifically to a UE, the UE needs to find out where its NR-PDCCH is. In the so-called “blindly” decoding process, the UE must try a number of candidate NR-PDCCHs before knowing which NR-PDCCH is targeted for itself. The allocated radio resources of the candidate NR-PDCCHs may be distributed or localized. In addition, the NR-PDCCHs may constitute a common search space (CSS) or a UE-specific search space (UESS). As a result, the aggregated radio resources of candidate NR-PDCCHs for different UEs may be different. In other words, NR-PDCCH may be UE-specific and it is beneficial for blind decoding. With UE-specific NR-PDCCH transmission, the size of search space for each UE can be reduced for smaller number of blind decoding candidates.
To reduce false alarm rate of NR-PDCCH decoding, the DCI information bits are attached with CRC bits, and the CRC attachment is masked by UE ID. Alternatively, a scrambling sequence initiated by UE ID is generated and scrambled to the DCI information bits. However, both methods are equivalent in false alarm rate. Applying a scrambling sequence does not address the false detection problem. A solution to improve the design of NR-PDCCH transmission and to reduce the false alarm rate of NR-PDCCH blind decoding is sought.